In related art, a mechanical cam has been used in manufacturing facilities in many fields. The mechanical cam is so configured that a disk-shaped cam is directly connected to a rotating body under measurement and a contact piece that is in contact with the cam provides a predetermined timing signal (switch signal) that follows the shape of the cam. The mechanical cam, however, is prone to wear of the cam and positional shift thereof, and cumbersome work, such as cam reproduction processing and position adjustment, is therefore required.
On the other hand, for example, Japanese Patent Laid-Open Patent Application No. 2007-76672 employs an electronic method, so to speak, using a resolver and a variable cam switch attached to the rotating shaft to provide the switch signal described above. That is, the resolver outputs predetermined reference voltage to the variable cam switch, and the variable cam switch outputs a switch signal according to the angle of rotation (rotational position) of the rotating shaft to a control apparatus (control panel) that serves as a high-level apparatus.